The present invention generally relates to an atrial defibrillator which detects an atrial fibrillation episode and responsive to such detection, applies cardioverting electrical energy to the atria of a human heart. The present invention more particularly relates to such an atrial defibrillator which further selectively stores heart activity data related to the detection of the atrial fibrillation episode. The selectively stored data includes data relating to the initial detection of the atrial fibrillation episode and data relating to the successful cardioversion of the atria. The selectively stored data may further include data relating to a synchronization protocol implemented by the atrial defibrillator immediately prior to the successful cardioversion of the atria.
Atrial fibrillation is probably the most common cardiac arrhythmia. Although it is not usually a life threatening arrhythmia, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. In addition, patients afflicted with atrial fibrillation generally experience palpitations of the heart and may even experience dizziness or even loss of consciousness.
Atrial fibrillation occurs suddenly and many times can only be corrected by a discharge of electrical energy to the heart through the skin of the patient by way of an external defibrillator of the type well known in the art. This treatment is commonly referred to as synchronized cardioversion and, as its name implies, involves applying electrical defibrillating energy to the heart in synchronism with a detected ventricular electrical activation (R wave) of the heart. The treatment is very painful and, unfortunately, most often only results in temporary relief for patients, lasting but a few weeks.
Drugs are available for reducing the incidence of atrial fibrillation. However, these drugs have many side effects and many patients are resistant to them which greatly reduces their therapeutic effect.
Implantable atrial defibrillators have been proposed to provide patients suffering from occurrences of atrial fibrillation with relief. Unfortunately, to the detriment of such patients, none of these atrial defibrillators have become a commercial reality.
Implantable atrial defibrillators proposed in the past have exhibited a number of disadvantages which probably has precluded these defibrillators from becoming a commercial reality. Two such proposed defibrillators, although represented as being implantable, were not fully automatic, requiring human interaction for cardioverting or defibrillating the heart. Both of these proposed defibrillators require the patient to recognize the symptoms of atrial fibrillation with one defibrillator requiring a visit to a physician to activate the defibrillator and the other defibrillator requiring the patient to activate the defibrillator from external to the patient's skin with a magnet.
An improved atrial defibrillator which does provide automatic operation is fully disclosed in U.S. Pat. No. 5,282,837 entitled IMPROVED ATRIAL DEFIBRILLATOR AND METHOD and which issued on Feb. 1, 1994 in the names of John M. Adams and Clifton A. Alferness. This patent is assigned to the assignee of the present invention and is incorporated herein by reference.
In addition to being automatic in operation, the atrial defibrillator of the above-referenced patent includes further features to assure the safe operation of the device. For example, to assure that the cardioverting electrical energy is not applied during the T wave vulnerable period of the heart, the atrial defibrillator provides R wave detection of increased reliability which is utilized to advantage in synchronizing the delivery of the cardioverting electrical energy to the atria with an R wave of the heart. Further, as another feature, an electrode system is utilized which minimizes the amount of energy that is applied to the ventricles during the cardioversion of the atria. This is achieved by locating the cardioverting electrodes in or near the heart to provide a cardioverting energy path which confines substantially all of the cardioverting electrical energy to the atria of the heart. This further reduces the risk of inducing ventricular fibrillation during the delivery of the cardioverting electrical energy to the atria of the heart.
Further improvements directed to the safe operation of an implantable automatic atrial defibrillator are described in U.S. Pat. No. 5,207,219 which issued on May 4, 1993 for ATRIAL DEFIBRILLATOR AND METHOD FOR PROVIDING INTERVAL TIMING PRIOR TO CARDIOVERSION and which is also assigned to the assignee of the present invention and incorporated herein by reference. The atrial defibrillator there disclosed provides an answer to the observation that during episodes of atrial fibrillation, the cardiac rate increases to a high rate and/or becomes extremely variable. At high or variable cardiac rates, the R wave of a cardiac cycle may become closely spaced from the T wave of the immediately preceding cardiac cycle. This creates a condition known in the art as an "R on T" condition which is believed to contribute to induced ventricular fibrillation if the atria are cardioverted in synchronism with the R wave close to the preceding T wave. In order to prevent cardioversion of the atria during an R on T condition, the atrial defibrillator described in U.S. Pat. No. 5,207,219 detects for a cardiac interval longer than a minimum interval prior to delivering the cardioverting electrical energy to the atria. This assures that the cardioverting electrical energy is not delivered during an R on T condition.
As can be seen from the foregoing, there is certain information related to atrial fibrillation and the cardioversion thereof from which the cardiologist would benefit. Such information includes activity of the heart during fibrillation to confirm proper operation of the atrial fibrillation detector, the activity of the heart prior to cardioversion and the activity of the heart from immediately prior to and ending after the deliverance of the cardioverting electrical energy to the atria to confirm that the application of the cardioverting electrical energy was synchronized with an R wave and not on a T wave and to also confirm that the cardioversion was successful by returning the heart to normal sinus rhythm. In order to provide such information, the implantable automatic atrial defibrillator would be required to store data, preferably representative of electrocardiograms of the heart.
The present invention provides such an implantable automatic atrial defibrillator capable of storing such information. More particularly, the atrial defibrillator of the present invention stores digital samples representative of selected electrocardiograms related to the detection of an atrial fibrillation episode and the successful cardioversion of the detected atrial fibrillation episode.